1. Field of Invention
The invention relates to an exhaust system of an internal combustion engine.
2. Description of Related Art
Generally an engine (internal combustion engine) for a vehicle is provided with an exhaust system formed of such components as an exhaust pipe, a catalytic converter and a muffler arranged therein. Especially in the case where the internal combustion engine is of V type, horizontally-opposed type and the like, which has two banks, the exhaust pipe including an exhaust manifold is connected to each of those two banks such that two exhaust pipes are connected to a muffler provided at a downstream side. The structure of the aforementioned exhaust system is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-200854.
In the exhaust system of the internal combustion engine as disclosed in the above-described publication, each base end portion of the exhaust pipes is connected to each of those two banks such that the exhaust gas is fed into the muffler through the respective exhaust pipes. The exhaust gas fed from each of the exhaust pipes joins within the muffler. The length of one of the exhaust pipes from its base end portion to an opening is substantially the same as that of the other exhaust pipe. The thus structured exhaust system prevents generation of noise or deterioration of the output caused by the difference in the length between those exhaust pipes owing to the limitation in the arrangement of the muffler.
Some driver or occupants of the vehicle may prefer powerful engine sound or the resultant exhaust sound, which is generated by the V-type engine or the horizontally-opposed type engine in accordance with the number of cylinders. The engine sound or the exhaust sound, accordingly may become one of key factors which drive the customer to buy the vehicle. It has been generally required, however, to reduce the engine sound or the exhaust sound as minimum as possible so as to reduce the undesired sound and vibration inside and outside the vehicle. Accordingly the above-structured system fails to allow the driver or the occupant to experience the powerful original sound of the engine or the resultant exhaust sound.
The way how the engine sound is transmitted to the muffler may vary to a certain extent depending on the length of the exhaust pipe from the bank to the muffler. In the above-structured system having the two exhaust pipes each of which has the same length, the sound quality with half order is likely to be erased, and accordingly, it is difficult to freely adjust (tune) the tone quality within the muffler.